This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-287544 filed on Sep. 20, 2001 and Japanese Patent Application No. 2000-327288 filed on Oct. 26, 2000.
1. Field of the Invention
The present invention relates to an infrared sensor and, more particularly, to a design of a sensing area including thermocouples and an infrared absorbing film in the sensor.
2. Description of the related Art
In general, an infrared sensor includes a concavity made on a side of a semiconductor substrate and a plurality of sensing areas formed in a thin film area at the back side of the bottom of the concavity. The sensor makes it possible to quickly measure the temperature of an object without making contact with the object. Additionally, the sensing areas have a boundary with the substrate in the periphery of the thin film area which is susceptible to heat loss due to heat conduction of the substrate. Therefore, the sensing areas in the periphery of the thin film area have a greater thermal capacity than the sensing areas in the central part of the thin film. Thus, the proposed sensor has a sensitivity deviation among the sensing areas.
Thus, it is an objective of the present invention to provide an infrared sensor that has a reduced sensitivity deviation among the sensing areas. That is, a more consistent thermal conduction of the sensing areas is desired.
According to the present invention, it is possible to generate greater electromotive force in the sensing area having a boundary with the substrate by means described hereinafter.
More thermocouples are provided in the sensing areas having a boundary with the substrate than in the sensing areas having no boundary with the substrate. The difference in the number of thermocouples between those sensing areas compensates for the heterogeneity of heat transfer in the thin film area due to the heat loss of the sensing areas having a boundary with the substrate. Therefore, the sensitivity becomes homogeneous among the sensing areas.
A larger infrared absorbing film is formed in the sensing area having a boundary with the substrate as compared to the sensing area having no boundary with the substrate. The difference in size of the film between those sensing areas compensates for the heterogeneity of heat transfer in the thin film area caused by the heat loss of the sensing area having the boundary with the substrate. Therefore, the sensitivity becomes homogeneous among the sensing areas.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.